SGS Thomson Microelectronics UC3845N, UC3845D, UC3843D, UC3844D, UC3844N Datasheet

	UC2842/3/4/5
	UC3842/3/4/5
	CURRENT MODE PWM CONTROLLER

.OPTIMIZED FOR OFF-LINE AND DC TO DC

.CONVERTERS

.LOW START-UP CURRENT (< 1 mA) AUTOMATIC FEED FORWARD COMPENSA-

.TION

.PULSE-BY-PULSE CURRENT LIMITING ENHANCED LOAD RESPONSE CHARAC-

.TERISTICS

UNDER-VOLTAGE LOCKOUT WITH HYSTER-

.ESIS

.DOUBLE PULSE SUPPRESSION

.HIGH CURRENT TOTEM POLE OUTPUT INTERNALLY TRIMMED BANDGAP REFER-

.ENCE

.500 KHz OPERATION LOW RO ERROR AMP

DESCRIPTION

TheUC3842/3/4/5family of controlICs providesthe necessary features to implement off-line or DC to DC fixed frequency current mode control schemes with a minimal externalparts count.Internallyimplementedcircuitsinclude undervoltagelockout featuring start-up current less than 1 mA, a precision reference trimmed for accuracy at the error amp input,

Minidip

SO14

logic to insure latched operation, a PWM comparatorwhich also providescurrentlimit control,and a totem pole output stage designed to source or sink high peak current. The output stage, suitable for driving N-Channel MOSFETs, is low in theoff-state.

Differences between members of this family are the under-voltage lockout thresholds and maximum duty cycle ranges. The UC3842 and UC3844 have UVLO thresholds of 16V (on) and 10V (off), ideally suited off-line applications The corresponding thresholds for the UC3843 and UC3845 are 8.5 V and 7.9 V. The UC3842 and UC3843 can operate to duty cycles approaching 100%. A range of the zero to < 50 % is obtained by the UC3844 and UC3845 by the additionof an internal toggle flip flop which blanks the output off every other clock cycle.

BLOCK DIAGRAM (toggle flip flop used only in U3844 and UC3845)

October 1998

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UC2842/3/4/5-UC3842/3/4/5

ABSOLUTE MAXIMUM RATINGS

Symbol	Parameter	Value	Unit
Vi	Supply Voltage (low impedance source)	30	V
Vi	Supply Voltage (Ii < 30mA)	Self Limiting
IO	Output Current	±1	A
EO	Output Energy (capacitive load)	5	μJ
	Analog Inputs (pins 2, 3)	± 0.3 to 6.3	V
	Error Amplifier Output Sink Current	10	mA
Ptot	Power Dissipation at Tamb ≤ 50 °C (minidip, DIP-14)	1	W
Ptot	Power Dissipation at Tamb ≤ 25 °C (SO14)	725	mW
Tstg	Storage Temperature Range	± 65 to 150	°C
TL	Lead Temperature (soldering 10s)	300	°C
* All voltages are with respect to pin 5, all currents are positive into the specified terminal.
PIN CONNECTIONS (top views)
	SO14	Minidip

ORDERING NUMBERS

T ype	Min idip	SO14
UC2842	UC2842N	UC2842D
UC3843	UC2843N	UC2843D
UC2844	UC2844N	UC2844D
UC2845	UC2845N	UC2845D
UC3842	UC3842N	UC3842D
UC3843	UC3843N	UC3843D
UC3844	UC3844N	UC3844D
UC3845	UC3845N	UC3845D

THERMAL DATA

Symbol	Descri pti on		Min id ip	SO14	Uni t
Rth j-amb	Thermal Resistance Junction-ambient.	max.	100	165	°C

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UC2842/3/4/5-UC3842/3/4/5

ELECTRICAL CHARACTERISTICS (Unless otherwise stated, these specifications apply for -25 < Tamb < 85°C for UC2824X; 0 < Tamb < 70°C for UC384X; Vi = 15V (note 5); RT = 10K; CT = 3.3nF)

Symbo l			Parameter	T est Cond ition s								UC284X			UC384X			Uni t
												Mi n. T yp. Max. Min. Typ . Max.
				REFERENCE SECTION
V	REF		Output Voltage						°			4.95	5.00	5.05	4.90	5.00	5.10	V
				Tj = 25 C Io = 1mA
VREF			Line Regulation		12V ≤ Vi ≤ 25V								6	20		6	20	mV
VREF			Load Regulation			1 ≤ Io ≤ 20mA							6	25		6	25	mV
VREF/ T			Temperature Stability					(Note 2)					0.2	0.4		0.2	0.4		°
																		mV/ C
			Total Output Variant	Line, Load, Temperature (2)								4.9		5.1	4.82		5.18	V
e			Output Noise Voltage	10Hz	≤	f	≤				°		50			50		μ	V
		N							10KHz Tj = 25 C
									(2)
			Long Term Stability						°				5	25		5	25	mV
				Tamb = 125 C, 1000Hrs (2)
ISC			Output Short Circuit									-30	-100	-180	-30	-100	-180	mA
				OSCILLATOR SECTION
	f	s	Initial Accuracy			Tj				°		47	52	57	47	52	57	KHz
								= 25 C (6)
			Voltage Stability			12 ≤ Vi ≤ 25V							0.2	1		0.2	1	%
			Temperature Stability	TMIN ≤ Tamb ≤ TMAX (2)									5			5		%
V4			Amplitude	VPIN4 Peak to Peak									1.7			1.7		V
				ERROR AMP SECTION
V2			Input Voltage			VPIN1 = 2.5V						2.45	2.50	2.55	2.42	2.50	2.58	V
	Ib		Input Bias Current										-0.3	-1		-0.3	-2	μA
			AVOL			2 ≤ Vo ≤ 4V						65	90		65	90		dB
	B		Unity Gain Bandwidth						(2)			0.7	1		0.7	1		MHz
SVR			Supply Voltage Rejection		12V ≤ Vi ≤ 25V							60	70		60	70		dB
	Io		Output Sink Current	VPIN2 = 2.7V						VPIN1 = 1.1V		2	6		2	6		V
	Io		Output Source Current	VPIN2 = 2.3V VPIN1 = 5V								-0.5	-0.8		-0.5	-0.8		mA
			VOUT High			VPIN2 = 2.3V;						5	6		5	6		V
				RL = 15KΩ to Ground
			VOUT Low			VPIN2 = 2.7V;							0.7	1.1		0.7	1.1	V
				RL = 15KΩ to Pin 8
				CURRENT SENSE SECTION
GV			Gain					(3 & 4)				2.85	3	3.15	2.8	3	3.2	V/V
V3			Maximum Input Signal			VPIN1 = 5V (3)						0.9	1	1.1	0.9	1	1.1	V
SVR			Supply Voltage Rejection		12 ≤ Vi					≤ 25V (3)			70			70		dB
	Ib		Input Bias Current										-2	-10		-2	-10	μA
			Delay to Output										150	300		150	300	ns
					OUTPUT SECTION
IOL			Output Low Level			ISINK = 20mA							0.1	0.4		0.1	0.4	V
					ISINK = 200mA								1.5	2.2		1.5	2.2	V
IOH			Output High Level	ISOURCE = 20mA								13	13.5		13	13.5		V
					ISOURCE = 200mA							12	13.5		12	13.5		V
	t		Rise Time			°				CL = 1nF	(2)		50	150		50	150	ns
		r		Tj = 25 C
	t		Fall Time			°				CL = 1nF	(2)		50	150		50	150	ns
		f		Tj = 25 C

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; 0 ≤ VPIN3 ≤ 0.8 V

UC2842/3/4/5-UC3842/3/4/5

ELECTRICAL CHARACTERISTICS (continued)

	Symbo l	Parameter	T est Cond ition s		UC284X		UC384X			Unit
				Min. T yp. Max. Min. T yp. Max.
		UNDER-VOLTAGE LOCKOUT SECTION
		Start Threshold	X842/4	15	16	17	14.5	16	17.5	V
			X843/5	7.8	8.4	9.0	7.8	8.4	9	V
		Min Operating Voltage	X842/4	9	10	11	8.5	10	11.5	V
		After Turn-on	X843/5	7.0	7.6	8.2	7.0	7.6	8.2	V
			PWM SECTION
		Maximum Duty Cycle	X842/3	93	97	100	93	97	100	%
			X844/5	46	48	50	47	48	50	%
		Minimum Duty Cycle				0			0	%
			TOTAL STANDBY CURRENT
	Ist	Start-up Current			0.5	1		0.5	1	mA
	Ii	Operating Supply Current	VPIN2 = VPIN3 = 0V		11	20		11	20	mA
	Viz	Zener Voltage	Ii = 25mA		34			34		V

N otes : 2. These parameters, although guaranteed, are not 100% tested in production.

3.Parameter measured at trip point of latch with VPIN2 = 0.

4.Gain defined as :

VPIN1

A =

VPIN3

5.Adjust Vi above the start threshold before setting at 15 V.

6.Output frequency equals oscillator frequency for the UC3842 and UC3843. Output frequency is one half oscillator frequency for the UC3844 and UC3845.

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